Amazon has Pilot Iroshizuku Bottled Fountain Pen Ink, Kon-Peki, Deep Cerulean Blue, 50ml, for $15.79 (with free Saver shipping if order is over $25, or Prime shipping). It says list price is $25, but you usually find it for $20 at other online pen shops.
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Other colors are available, at varying prices, but none at this price. A couple others are "okay" deals at about $18 — Shin-Ryoku (deep green), Kosumosu (pink)
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